Stadiametric range finder



HHM: VA

c. A. MORRISON STADIAMETRIC RNG'FINDER July 8, 1947.

BY Z

A TTORNE YS lil( Patented July S, 1947 42ans S'L'ADAMETIC RANGE FENDER Charles A. Morrison, Rochester, N. Y., assigner to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application February 20, 1946, Serial No. 648,973

./j claims. (Cisa-2.3)

This invention relates to stadiametric range finders. A stadiametric range nder is one which is used for ranging on targets of known diameter .I a 2 I Fig. 2 is a plan View partly in section of the embodiment shown in Fig. 1. l

Fig. 3 similarly illustrates another embodiment of the invention.

such as a known ship or a known type of airplane.

providing a range reticle, In this sense, the purpose of the present invention is to provide a reticle producing means alternative to that described in U. S. 2,360,822 Altman.

Specifically it is the object of the present invention to provide a device for producing a complete ring of light of variable diameter. One particular advantage of the invention is the fact that the sensitivity or response of the instrument, thatis to say, the amount of change of reticle diameter with movement of the adjusting mechanism, may be selected at will.

It is known that a point of light viewed through a solid cone of transparent refractive material will appear as a ring if the geometric axis of the cone passes through or near the point of light. According to the present invention this principle is applied to stadiametric range finders by using a cone of glass or other transparent material having very wide apex angle between 150 and 180 and by moving the cone nearer or farther from the spot of light in order to vary the apparent diameter of the ring of light. Qptical means are provided for superimposing this ring of light ona real or virtual image of the target being ranged. The adjustment o f the cone is thus a direct measure of the range of thev target, provided of course that the diameter ofthe target itself is known as is necessary with all stadiametric ranging devices. i

If the apex angle of the cone is nearly 180, the diameter of the reticle changes very 1ittle as the cone is adjusted axially, whereas the response is much greater with cones having smaller apex 'l angles. That is, the sensitivity and accuracy of the device is inversely proportional to the power of the conical lens.

The operation of the invention will be fully understood from the following description of the preferred embodiments thereof, when read in connection with the accompanying drawing in which:

Fig. 1 is a perspective view of an optical system incorporating one embodiment of the invention.

In Fig. l light from a target l0 to be ranged is focused by an objective lens Il to form an image I3 on the rear surface of a beam combining block l2. This image may be viewed through an eyepiece lll by the eye I5 of an observer. According to the present invention, light from a lamp I6 with a suitable reflector I1 and condenser lens i8 illuminates a small hole 2li in an opaque mask l 9, the small hole 20 acting as a secondary source of light. A conical lens 2i causes this hole of light to appear as a ring except when the lens 2l is at the mask I9 itself, at which time this spot of course appears just as a spot. An image of the spot or ring is formed by lens 22 and semitransparent reflecting surface 23, superimposed on the target image. In Fig. 1 this image of the ring is shown as 2li. The operation of the conical lens 2l is perhaps best seen in Fig. 2, where the rays El after passing through the lens 2l appear as if coming from a ring 43. That is the rays il appear to come from this ring as indicated by the broken line 2. The ring is thus a virtual image of the spot, formed by the conical lens 2|.

In order to provide adjustment of the diameter of this ring for stadiametric ranging, the conical lens 2l is carried in a mount 30 which is free to slide axially in the housing lli ofthe range finder. Adjustment is made manually by moving the knob 3l which is connected through a slot in the housing to the lens mount 30. The knob 3l carries the pointer- 33 which moves along a scale 32 on the housing. The range factor read from this scale gives the range directly when the diameterA of the target is known. Calibration forwaiious target diameters may be provided in any of the usual ways for example by a suitable graph. The

scale 32 and index 33 are merely representative of the various forms of range indicative devices used in range finders. For example certain range finders feed the range data directly into some computing mechanism rather than to a scale to be read visually.

While Figs. 1 and 2 illustrate the preferred embodiment of the invention in which the ranging circle is superimposed on a real image of the target to be ranged, Fig. 3 shows an alternative arrangement in which the target is viewed relatively directly and a virtual image of the ranging circle is superimposed thereon. Light 5B from the target being ranged passes through a beam combiner 5l to the eye of the observer. Simulffr -aj .t

taneously with this light: the eye receives light from the reticle as collimated by an objective 52 and as formed into a ring by a conical lens 53 according to the invention. The spot of light is provided by an aperture 54 in an opaque mask illuminated by a flashlight lamp 55 which receives its power from a flashlight battery 51, the lamp being turned on and off at will by a suitable switch 56. The conical lens 53 in its mount Si) is carried 0n a suitable rack which engages a pinion 6I which in turn is rotated by a ranging knob G2. Strictly speaking, the observer does not see the target directly since he is looking through a light refractive material which carries the beam combiner 5I and hence it is proper to refer to the reticle image being superimposed on the target image. Alternatively it may be simpler to think of the term target image as being generic to the targetl itself as Well as real and virtual images thereof and it is so used in this specification and the accompanying claims.

I claim:

5A of light, a solid conical lens 0f transparent refrac- Y;tive material in line with light from the spot, the j* apex angle of the cone being between 150 and 180", the axis of the cone being substantially aligned with said spot, means for holding the loollllllgng and for moving it axially in the 'housing to and from the spot of light whereby the spot appears through the cone as a ring of light of variable diarneterl means including an objective for receiving light from the spot through 15 the cone and for projecting an image of said ring in the comparison plane and range indicative means operated by said cone moving means.

2. A range finder according to claim 1 in which is included means for forming a real image of the 20 target to be ranged in the comparison plane and an eyepiece for viewing the comparison plane.

' CHARLES A. MORRISON. 

